Bukkit

Hello, ive been using this plugin for a modded minecraft server. Im using magma, it works well, but sometimes players disconnect and trying to come back they find an error:

"Failed to connect to the server. Another player is already online with this name."

But theres no one online with that name, trying to force the kick or doing it from the console doesn´t work. The second error happens randomly, the server kicks the player and the player cant reconect

"Connection Lost: Internal Exceptions: io.netty.handler.codec.DecoderException: Java.lang.IndexOutOfBoundsException: readerIndex(51) + lenght(2) exceeds writerIndex(51): PooledUnsafeDirectByteBuf(ridx: 51, widx: 51, cap:51) "